1. Field of the Invention
The present invention relates to a process for the production of yeast extracts.
2. Description Of Related Art
Yeast extracts are commonly used in the food industry to improve or enhance the flavour of all sorts of savoury food applications such as in soups, crisps, chips, (processed) meats, etceteras.
The Food Chemical Codex defines a “yeast extract” as follows: “Yeast Extract comprises the water soluble components of the yeast cell, the composition of which is primarily amino-acids, peptides, carbohydrates and salts. Yeast extract is produced through the hydrolysis of peptide bonds by the naturally occurring enzymes present in edible yeast or by the addition of food-grade enzymes”. In contrast, the same Food Chemical Codex defines “autolysed yeast” as “the concentrated, nonextracted, partially soluble digest obtained from food-grade yeast. Solubilization is accomplished by enzyme hydrolysis or autolysis of yeast cells. Food-grade salts and enzymes may be added. Yeast, autolyzed, contains both soluble and insoluble components derived from the whole yeast cell. It is composed primarily of amino acids, peptides, carbohydrates, fats, and salts”. A yeast autolysate therefore differs from a “yeast extract” because the yeast autolysate, in addition to all the interesting components present in yeast extracts, also contains interesting cell wall components which are not separated from the soluble fraction.
Yeast extracts are generally produced by:                a) subjecting a yeast to autolysis; and        b) subjecting the autolysate to solid/liquid separation and recovering the liquid fraction.        
Usually such a process starts with a cream yeast which is obtained by removing the waste liquor after harvesting of the yeast cells at the end of a fermentation, i.e. by removing the vinasse. Next, the yeast cells in the cream yeast are treated such that the cells are disrupted and contents are released. This is generally done by two different processes, resulting in either autolytic yeast extracts or hydrolytic yeast extracts.
Autolytic yeast extracts are concentrates of the soluble materials obtained from yeast after disruption of the cells and digestion (lysis) of the polymeric yeast material. The active yeast enzymes released in the medium after cell disruption are responsible for the lysis. Generally these types of yeast extracts do not comprise 5′-ribonucleotides because during the autolytic process the native RNA is decomposed or modified in a form which is not or almost not degradable into 5′-ribonucleotides. These types of yeast extract, which are rich in amino acids, are used in the food industry as basic taste providers. The amino acids present in the yeast extract add a bouillon-like, brothy taste to the food.
Hydrolytic yeast extracts, on the other hand, are concentrates of the soluble materials obtained from yeast after disruption of the cells, digestion (lysis) and addition of proteases and/or peptidases and especially nucleases to the yeast suspension during lysis. The native yeast enzymes are inactivated prior to the lysis, generally by a heat shock.
A problem with yeast extracts obtained by processes known in the art is that they may be turbid when dissolved, which can be a disadvantage in clear applications such as clear soups and the like. A possible solution for this turbidity is to apply extra filtration steps such as ultrafiltration or microfiltration. However, not only is this not economical since it requires additional process steps, but it also leads to losses since the material which causes the turbidity stays behind the filter and is discarded.